Most other DE's and even just regular WM's when used with feh can use a single large wallpaper spanning multiple screens, eg 5760x1080 for triple head. KDE 5 however can not do this and it also blocks feh from working as well. This used to work with KDE 3 and earlier but appears to have broken since then with the rewrite. I wasn't sure which component was the better fit, Image Wallpaper or Multi-screen support so put it under Image Wallpaper since that is likely where it needs to be fixed. https://feh.finalrewind.org/
This is a couple of years old now, but I too would like to see this implemented. Just as an fyi, there is an external program that will accomplish this in the meantime: superpager. It's a little geeky on the interface, but it gets the job done.
*** Bug 436785 has been marked as a duplicate of this bug. ***
A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-workspace/-/merge_requests/1800
What if, rather than another Positioning option as proposed in the above MR, a boolean setting was added to span screens? It could be placed at the end of this form layout so it applies to all Positioning options: https://github.com/KDE/plasma-workspace/blob/0fa3bbc4c63e84d5902e0950e4fa0559fe1988cf/wallpapers/image/imagepackage/contents/ui/config.qml#L90 If set to true, make the calculation for the wallpaper based on the dimensions of the entire desktop, rather than the single screen, then crop it to that screen's portion of the desktop based on its x, y, w & h. The exception is the Tiled option where it could simply change the offsets. It looks like the necessary dimensions are exposed: https://doc.qt.io/qt-5/qscreen.html#virtualGeometry-prop and its virtualGeometryChanged signal would allow the wallpaper to be "re-sliced" upon layout changes.
Feel free to submit a merge request. The original author of the MR above is unable to continue the work.
*** Bug 488105 has been marked as a duplicate of this bug. ***
I think this would be a great feature also. I'm about to get 3 identical 4K monitors and having one really hi-res wallpaper across all 3 screens would look fantastic. I'm not a programmer but I wouldn't think this option would be a horrendous amount of work and seems like quite a few folks would appreciate it.
I, too, would appreciate something like this working. There is Superpaper, (https://github.com/hhannine/superpaper) which with some doing can even work on Wayland (https://github.com/hhannine/superpaper/issues/150), but it's still not a native Wayland app. Still, the code is there, and it's open source. So perhaps someone could one day add it to KDE? Wish I could do it myself but I'm no programmer.
I support the request too. I miss the single desktop that spans multiple monitors since the days, xinerama has gone. I use 3 monitors in portrait mode and I would not only be happy about a common background, but also about the ability to maximize a window across all monitors. I know that the opponents of the shared desktop argue with the different monitor sizes that may be supported. I would therefore be happy if the shared desktop would be optional, so that each user may decide for themselves whether they want it or not.
Adding a bump to the requests for this feature. I have had a single image wallpaper spread across 3 screens on my desktop for years on Windows. It's surprising to find this feature missing in KDE which is otherwise a far more customisable and full-featured system.
I built a tool once to do this specifically for KDE. Its a bit buggy and you have to compile it yourself, but it might help some folks here or serve as a reference implementation: https://github.com/l0drex/WallpaperSplitter